Recent siRNA Research Publications Support Silence Therapeutics
Combined Development Approach

LONDON, April 07, 2008, 2008 /PRNewswire/ -- Silence
Therapeutics plc (AIM:SLN) Europe's leading RNAi-focused
biotechnology company, today comments on two recent journal
articles: Nature(1) "Sequence-and target-independent angiogenesis
suppression by siRNA via TLR3" Mark E. Kleinman, et. al., and
Molecules and Cells(2) "Immune Activation by siRNA/Liposome
Complexes in Mice is Sequence-Independent: Lack of a Role for
Toll-like Receptor 3," Kim et. al. In these two publications,
researchers questioned current thinking on the mode of action of
siRNA therapeutics suggesting that they work by mechanisms other
than via specific gene silencing.

Data published in the Nature article (Kleinman et. al.) have
been interpreted in recent days in the lay press as a "Setback for
Some RNA-Based Drugs" ((5)). Silence Therapeutics views the cited
Nature paper, and another recent paper in Molecules and Cells(2) as
highlighting the need for a functional delivery system to ensure
the therapeutic siRNA is able to enter cells and achieve gene
silencing.

Both studies further reinforce the importance of chemically
modifying siRNA to create molecular structures which do not cause
unwanted immune stimulation such as cytokine release and interferon
response.

The two new studies support the long-standing development
approach of Silence Therapeutics, which has focused its research on
developing both a potent RNAi-mediating delivery system (AtuPLEX)
and chemically-modified siRNA (AtuRNAi) molecules.

Jeff Vick, CEO of Silence Therapeutics, said, "More than eight
years ago, Silence Therapeutics recognized the need for, and
pioneered the development of, a functional systemic RNAi delivery
system that combines proprietary chemical modification and lipid
technologies to achieve efficient intracellular uptake without
triggering an immune system response. This approach has allowed us
to successfully demonstrate the inhibition of solid tumor growth
and the spread of metastases. Silence continues to develop
additional delivery technologies to broaden the clinical
applications of our promising new class of siRNA therapeutics."

Silence Therapeutics has previously reported in 2006, in two
peer reviewed publications in Gene Therapy(3,4), the functional in
vivo delivery of different AtuRNAi-lipoplexes (chemically modified
siRNA molecules formulated in a proprietary lipid complex). In
particular, Silence Therapeutics' AtuPLEX formulation was shown to
both avoid immune responses (published data demonstrates lack of
activation of interferon-alpha and IL-12) and induce RNAi-mediated
gene silencing as demonstrated by the selective inhibition of
endogenous target-specific gene expression in vivo. Furthermore,
independent publications by Judge(6) and Kim(2) also demonstrate
that the chemical modification modality utilized in AtuRNAi
obviates an immune response.

These Gene Therapy papers also show that the target-specific
knockdown (gene silencing) resulted in the modulation of a specific
biochemical signaling pathway containing the target, thus
demonstrating the potential therapeutic benefits in certain
oncology indications.

The multi-faceted approach that Silence Therapeutics has taken
to realize the enormous potential of siRNA therapeutics was
substantiated by Dr. Alan Sachs, Vice President for RNA
Therapeutics at Merck Research Laboratories, a unit of Merck, who
was quoted in the ,(5) saying that "future versions of RNA drugs
could be encapsulated in fat globules and chemically modified. That
would help the drugs enter cells and keep them from setting off the
immune system."

Jeff Vick further commented, "That future is now. This is the
exact approach pioneered by Silence Therapeutics. Our current
pipeline is based on combining our state-of-the-art AtuRNAi
molecules and AtuPLEX drug delivery system. We have strong evidence
that the siRNA therapeutics we are developing do enter mammalian
cells, are appropriately localized intracellularly, and do act by
selectively silencing the specifically targeted gene. We believe by
continuing to build on this unique expertise we will achieve our
goal of becoming a global leader in the RNAi space."

Silence Therapeutics plc (AIM:SLN) is a leading RNAi company.
RNA interference (RNAi) can selectively 'silence' genes linked to
the onset of disease.

Silence Therapeutics has developed novel, proprietary short
interfering RNA ('siRNA') molecules, AtuRNAi, which provide a
number of advantages over conventional siRNA molecules as they show
increased stability against nuclease degradation. In addition, the
Company has developed a proprietary systemic delivery system,
AtuPLEX. This enables the delivery of siRNA molecules to targeted
diseased tissues and cells, whilst increasing their bioavailability
and intracellular uptake.

In July 2007, Silence Therapeutics formed a research and
development collaboration with AstraZeneca to develop AtuRNAi
against five specific targets including those in respiratory
indications. The Company's AtuRNAi technology also has been
sublicensed to Pfizer through Quark's license to Pfizer of the
compound RTP-801i-14 for the treatment of Age-related Macular
Degeneration (AMD) and a number of other indications. This compound
entered the clinic in early 2007. Silence Therapeutics also has
licensed to Quark rights to the AtuRNAi structure for its
proprietary compound AKIi-5. This compound is in a Phase I human
clinical study for treatment of acute kidney injury. In addition,
Silence Therapeutics expects to begin the clinical development of
its own proprietary AtuRNAi therapeutic molecules for systemic
cancer indications in 2008.

Silence Therapeutics is based in London, UK, and Berlin,
Germany, and is listed on AIM.